Layered heat exchangers

Abstract: A layered heat exchanger comprises pairs of generally rectangular adjacent plates (2), each of the plates being formed in one side thereof with a U-shaped channel recess (3) and a pair of header recesses (4) continuous respectively with one end and the other end of the channel recess and each having a fluid passing opening (8), the plates (2) being joined together in layers with the corresponding recesses (3) of the plates (2) in each pair opposed to each other to thereby form juxtaposed flat tubes (5) each having a U-shaped fluid channel, and front and rear headers communicating respectively with opposite ends of each flat tube (5) for causing a fluid to flow through all the flat tubes and headers. At least one of the adjacent plates (2) in each pair is provided with a U-shaped divided channel forming ridge (15,16) on a bottom wall of the channel forming recess, the pair of plates (2) being fitted and joined to each other with the corresponding recesses (3) opposed to each other to thereby form a plurality of U-shaped divided independent channels of reduced width inside the flat tube (5).

Description: BACKGROUND OF THE INVENTION The present invention relates to layered heat exchangers useful as evaporators for motor vehicle air conditioners. Document FR-A-813272 shows a known heat exchanger with adjacent plates which are formed with a U-shaped channel recess and a pair of header recesses. The adjacent plates are provided with a number of arcuate channel forming ridges on a bottom portion of the channel forming recess. The ridges on both sides of a central longitudinal axis of the channel recess are arranged symmetrically to said central longitudinal axis such that, with the plates joined together, the channel forming ridges are butted against and joined to each other to form a plurality of divided, independent, U-shaped channels of reduced width inside the flat tube. Already known as such layered heat exchangers are two types; those having headers at one of the upper and lower sides of an assembly of plates in layers, and those having headers at these sides, respectively. Those of the former type have a heat exchange portion which is greater than in the latter type and are therefore expected to exhibit improved performance. Stated more specifically, layered heat exchangers having the headers at one side comprise pairs of generally rectangular adjacent plates, each of the plates being formed in one side thereof with a U-shaped channel recess and a pair of header recesses continuous respectively with one end and the other end of the channel recess and each having a fluid passing opening, the plates being joined together in layers with the corresponding recesses of the plates in each pair opposed to each other to thereby form juxtaposed flat tubes each having a U-shaped fluid channel, and front and rear headers communicating respectively with opposite ends of each flat tube for causing a fluid to flow through all the flat tubes and the headers However, the conventional layered heat exchanger having tile headers at one side has the problem that when used as an evaporator for motor vehicle air conditioners, the refrigerant fails to flow smoothly along the turn portion of U-shaped channel recess of each plate and to achieve as high an efficiency as is expected. This is because if the plates are designed, for example, to produce a rectifying effect, the refrigerant flow pressure loss can be diminished, but a reduced heat transfer coefficient and therefore an impaired heat exchange efficiency will result, whereas if the plates are conversely adapted to give a mixing effect chiefly, the refrigerant flow pressure loss increases to an undesirable level despite an improved heat transfer coefficient. The refrigerant is then liable to stagnate or flow unevenly especially in the vicinity of U-shaped turn portion of the refrigerant channel of each flat tube, consequently permitting the evaporator to exhibit impaired performance. Further with the conventional evaporator, the joint between the plates is made by point contact, which therefore entails the problem that it is difficult to ensure pressure resistant strength. SUMMARY OF THE INVENTION The present invention provides a layered heat exchanger which is free of the foregoing problems. The heat exchanger of the present invention is characterized by the features of claim 1. With the heat exchanger described, the fluid flows through the flat tube without mixing between the adjacent divided channels and free of stagnation. Accordingly, vapor-liquid separation is confined to only one divided channel, therefore diminishes and will not entail an increased fluid pressure loss. The heat exchanger described can be in the following modes. First, the fluid inlet is provided at one end of the rear header, and the fluid outlet is provided at the other end of the front header, each of the front and rear headers being provided with at least one partition intermediately thereof, the partition being even in total number and arranged on the rear and front sides alternately when seen from above in the direction of from the fluid inlet toward the fluid outlet, to thereby form a zigzag fluid passage divided into an odd number of passageways including an inlet passageway, an outlet passageway and an intermediate passageway between the two passageways, the outlet passageway permitting the fluid to flow therethrough countercurrently against the flow of air. Second, the fluid inlet is provided at one end of the front header, and the fluid outlet is provided at the other end of the front header, each of the front and rear headers being provided with at least one partition intermediately thereof, the partitions being odd in total number and arranged on the front and rear sides alternately when seen from above in the direction of from the fluid inlet toward the fluid outlet, the partitions on the front header being one greater in number than on the rear header, to thereby form a zigzag fluid passage divided into an even number of passageways including an inlet passageway, an outlet passageway and an intermediate passageway between the two passageways, the outlet passageway permitting the fluid to flow therethrough countercurrently against the flow of air. The layered heat exchanger in any of the above modes is useful, for example, as a layered evaporator for use in motor vehicle air conditioners. Since the flow of refrigerant through the outlet passageway is countercurrent against the flow of air, the temperature difference between superheated refrigerant and air to be subjected to heat exchange therewith is greater than in evaporators of the concurrent type wherein the superheated refrigerant is positioned downstream with respect to the direction of flow of air. The portion wherein the refrigerant is in a superheated state therefore achieves a high heat exchange efficiency. Consequently, this portion of the refrigerant passage can be diminished to provide a larger portion for the refrigerant in the form of a vapor and to assure stabilized heat exchange performance. The invention will be described in greater detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective view of a heat exchanger as an embodiment of the invention; FIG. 1 is a view in vertical section of the heat exchanger; FIG. 3 is a perspective view of plates constituting the heat exchanger; FIG. 4 is an enlarged fragmentary front view showing the plate of flat tube of the heat exchanger; FIG. 5 is a view in horizontal section of the flat tube of the heat exchanger; FIG. 6 is an enlarged fragmentary front view partly broken away and showing a modified plate for use in the heat exchanger; FIG. 7 is a view in section taken along the line 23-23 in FIG. 6 ; FIG. 8 is a schematic perspective view of the refrigerant passage of heat exchanger of FIG. 1 DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the drawings, like parts are designated by like reference numerals. In this specification, the upstream side of flow of air will be referred to as "front," the downstream side thereof as "rear," and the terms "right" and "left" are used for the device as it is seen from the front rearward. FIGS. 1 to 5 and FIG. 8 show one embodiment of the invention, i.e., a layered evaporator 1. Each plate 2 of the evaporator 1 has a channel recess 3, which has a vertically elongated partition ridge 9 at the widthwise midportion thereof. The ridge 9 has the same height as the peripheral edge portion 19 of the plate 2 and extends from the upper end of the recess 3 to a position close to the lower end thereof. The recess 3 of the plate 2 has a multiplicity of ridges 15, 16 having a height twice the depth of the recess 3. While the evaporator 1 comprises pairsof adjacent plates 2, the ridges 15, 16 of each pair of plates 2, 2 as joined together form independent parallel U-shaped divided refrigerant passages inside a flat tube 5 provided by the pair. Stated more specifically with reference to FIG. 4, each ridge 15 (16) comprises a straight portion 15a (16a) provided in a front (rear) straight channel forming portion 3a (3b) of the recess 3, and a quarter circular-arc portion 15b (16b) provided in a turn portion 3c of the recess and continuous with the straight portion. The ridge has exactly one half of U-shape. When the pair of plates 2 are fitted together with their recessed 3, 3 opposed to each other, these straight portions 15a, 16a and the quarter circular-arc portions 15b, 16b of the ridges 15, 16 are arranged alternately. With the two plates 2, 2 fitted together, the opposed partition ridges 9, 9, as well as the opposed plate peripheral edge portions 19, 19, butt against and are joined to each other, and the straight portions 15a, 16a and circular-arc portions 15b, 16b of the ridges 15, 16 are joined at their top ends to the bottom wall 18 of recess of the plate 2 opposed thereto, whereby nine parallel U-shaped refrigerant passages as divided by the ridges 15, 16 are formed in the U-shaped refrigerant channel of the flat tube 5. The turn portion of each passage is semicircular. As shown in FIG. 5, the divided passages are nearly square in cross section so as to permit uniform distribution of liquid throughout the U-shaped refrigerant channel of the flat tube 5 and to ensure a joint area between the tube 5 and a fin 24. With respect to the cross sectional area of the divided passages, those positioned inward are-largest, outward passages are smallest, and intermediate passages are equal to one another or larger if closer toward inside. This renders the flow velocity uniform transversely of the channel. Generally triangular front and rear reinforcing projections 35 having the same height as the peripheral edge portion 19 of the plate 2 are provided respectively at the lower-end front and rear corners of the plate 2 (see FIGS. 3 and 4). Further as seen in FIG. 2 , each plate 2 has two header recesses 4, 4 each having a refrigerant passing opening 8. The opening 8 of one of the recesses 4 has an annular wall 26 formed by burring and projecting outward from the recess 4. When the opposed plates 2, 2 of each two adjacent flat tubes 5 are fitted together, in the front and rear headers 7, 6, the annular wall 26 around the opening 8 of the header recess 4 of one of the plates 2 is fitted in the opening 8 of the recess 4 of the other plate 2 opposed thereto. FIG. 8 shows the overall refrigerant passage of layered evaporator 1 of the described embodiment which will be described below. With reference to the drawing, a refrigerant inlet 41 is provided at the left end of rear header 6 of the evaporator 1, and a refrigerant outlet 42 at the right end of the front header 7. The rear header 6 has a partition 46 at a position rightwardly away from its left end by about 1/3 of the length of the header. The front header 7 has a partition 45 at a position leftwardly away from its right end by about 1/3 of the length of the header. The rear header partition 46 is formed by not forming the refrigerant passing opening in the recess of the plate 2 concerned. The front header partition 45 is formed similarly by not forming the opening. A refrigerant inlet pipe 30 has an opening corresponding to the refrigerant inlet 41, and a refrigerant outlet pipe 31 has an opening corresponding to the refrigerant outlet 42. A zigzag refrigerant passage 40 is thus formed which is divided into three passageways, i.e., an inlet passageway 40A, outlet passageway 40C and intermediate passageway 40B between the two passageways 40A, 40C, and in which the refrigerant flows through the outlet passageway in a countercurrent relation with the flow of air. The refrigerant is introduced into the rear header 6 through a feed pipe 27 and the inlet pipe 30 at the left side of the evaporator 1 (see FIG. 1 ) by way of the refrigerant inlet 41. The refrigerant is turned by the rear header partition 46 and flows through the inlet passageway 40A countercurrently against the air flow, is turned by the front header partition 45 and flows through the intermediate passageway 40B concurrently with the air flow, then flows through the outlet passageway 40C countercurrently against the air flow and is thereafter discharged from a discharge pipe 28 via the outlet 42. On the other hand, air flows in the direction of arrow X shown in the drawing, that is, from the front rearward to pass through the clearances between the adjacent flat tubes 5 and between each side plate 20 and the tube 5 adjacent thereto, the clearances having corrugated fins 24 accommodated therein, whereby the refrigerant and the air are efficiently subjected to heat exchange through the plates 2 and the fins 24. With the embodiment described, the refrigerant flows into the evaporator 1 as separated into a vapor and liquid, for example, in a volume ratio of 3:7. Inside the rear header 6, therefore, the liquid stays at a lower position due to a specific gravity difference, and the refrigerant flows into the flat tube 5 at an approximately uniform vapor-liquid distribution ratio with respect to the widthwise direction. Since the height of inner edge of the recess 3 is greater than that of the outer edge thereof, the vapor is caused to flow into the innermost divided refrigerant passage preferentially. The refrigerant boils within the flat tube 5 to result in an increasing vapor phase ratio. The refrigerant flows through the U-shaped refrigerant channel of each flat tube 5 without mixing between the adjacent divided passages and free of stagnation. Accordingly, vapor-liquid separation occurs in only one divided passage, therefore diminishes and will not entail an increased refrigerant pressure loss. The refrigerant smoothly flows especially through the turn portion, whereby an improved heat transfer coefficient can be attained. Further in the vicinity of the turn portion of the U-shaped flat tube 5, the refrigerant flows free of stagnation or irregular flows, while traces of oil contained in the refrigerant will not stay. Moreover, the difference in average temperature between the refrigerant and the atmosphere becomes diminished, leading to a further improved heat transfer coefficient. The partitions 45, 46 in the respective front and rear headers 7, 6 need not always be disposed at a position away from the right or left end by exactly 1/3 of the length of the headers, but the position can be suitably altered rightward or leftward with the heat exchange efficiency taken into consideration. Although the embodiment described has three passageways 40A to 40C, two partitions 45 and two partitions 46 may be provided in the front and rear headers 7, 6, respectively, as arranged alternately to provide five passageways including an outlet passageway wherein a countercurrent flow is produced against the air flow. An odd number of passageways, not smaller than 7 in number, can be used. FIGS. 6 and 7 shows a modified plate 2 for use in the evaporator 1 according to the described embodiment. With this modification, the ridges 15, 16 of the channel recess 3 of the plate 2 are separated into straight portions 15A, 16A and quarter circular-arc portions 15B, 16B, respectively, with the upper ends of the arc portions 15B, 16B displaced from the lower ends of the straight portions 15A, 16A by one-half of the ridge pitch. Such modified plates 2, 2 are fitted together with their recesses 3, 3, as well as the recesses 4, 4, opposed to each other, the central partition ridges 9, 9 opposed to each other, as well as the peripheral edge portions 19, 19 of the plates, are butted against and joined to each other, and the independent straight portions 15A, 16A and the quarter circular-arc portions 15B, 16B of the ridges 15, 16 are joined at their top ends to the bottom wall 18 of channel recess 3 of the plate 2 opposed thereto. Consequently, nine divided parallel U-shaped refrigerant passages are formed in the U-shaped refrigerant channel of the resulting flat tube 5 as in the case of the other embodiment. With the modification, the front and rear corners of the lower end of the plate 2 are provided with generally triangular front and rear reinforcing projections 35, 35, respectively, which have the same height as the plate peripheral edge portion 19. As shown in FIGS. 6 and 7, a bore 39 defined by an annular wall 38 is formed by burring in one of the projections 35, and the other projection 35 is formed with a hole 36 for the annular wall 38 to fit in. Accordingly when two plates 2, 2 are fitted and joined to each other, the annular wall 38 of the projection 35 of one of the plates is fitted into the hole 36 of the projection 35 of the other plate, whereby the adjacent plates 2, 2 can be accurately positioned relative to each other. This eliminates the need to crimp the peripheral edge portion of the plate 2 as conventionally done, making the plates accurately settable for brazing and positionable relative to each other within the furnace and obviating brazing faults and faults in the internal circuit due to positioning errors. In the front and rear headers 7, 6, and annular wall 26 around the refrigerant opening 8 is fitted into the opening 8 in the plate 2 opposed thereto. Thus, these fitting means prevent errors in positioning the plates 2 of the whole evaporator 1. The ridges 15, 16 provided on the plate 2 according to the foregoing embodiment or modification are not limited to those shown in shape but can be modified variously insofar as parallel U-shaped divided refrigerant passages can be formed in the assembly of the adjacent plates 2, 2. With the plates 2 of the described embodiment and the modification, the ridges 15, 16 are so disposed as to be alternately arranged in the assembly of adjacent plates 2, 2, and the U-shaped passages of the resulting flat tube 5 are arranged in the front and rear portions of the channel symmetrically as a whole, so that the number of ridges 15, 16 on the plate 2 can be smaller. This makes the plate 2 simple in configuration, easy to shape and less costly to manufacture. The ridges 15, 16 in the channel recess 3 of each plate 2 are joined at their top ends to the bottom wall 18 of recess 3 of the plate 2 opposed thereto. This affords an increased joint area, produces joints of line contact instead of spot-to-spot contact and leads to enhanced pressure resistant strength.

Claims: A layered heat exchanger comprising pairs of generally rectangular adjacent plates (2), each of the plates being formed in one side thereof with a U-shaped channel recess (3) and a pair of header recesses (4) continuous respectively with one end and the other end of the channel recess and each having a fluid passing opening (8), the plates (2) being joined together in layers with corresponding recesses (3) of the plates (2) in each pair being disposed in opposition to each other to thereby form juxtaposed flat tubes (5) each having a U-shaped fluid channel, and front and rear headers communicating respectively with opposite ends of each flat tube (5) for causing a fluid to flow through all the flat tubes and headers, the adjacent plates (2) in each pair being provided with a plurality of arcuate channel forming ridges (15,16) on a bottom portion of the channel forming recess, the adjacent plates (2) are fitted and joined to each other with the corresponding recesses opposed to each other to thereby form a plurality of U-shaped divided independent channels of reduced width inside the flat tube, the heat exchanger being characterized in that each of the ridges (15,16) provided in the refrigerant channel forming recesses of each plate comprises straight portions (15a,16a) provided in both front and rear straight channel forming portions (3a,3b) of the recess (3) and quarter circular-arc portions (15b,16b) provided in a turn portion (3c) of the recess (3), whereby the quarter circular-arc portions (15b,16b) are continuous with the straight portions (15a, 16a), or the straight portions (15a,16a) and the quarter circular-arc portions (15b,16b) are arranged alternately and the upper ends of the arc portions (15b,16b) are displaced from the lower ends of the straight portions (15a,16a) by one-half of the ridge pitch, the straight portions (15a,16a) and the arc portions (15b,16b) of the ridges (15,16) each having a top end butting against and joined to a bottom wall of the refrigerant channel forming recess (3) of the plate (2) opposed thereto.

Inventors: GO NOBUAKI, HANAFUSA TATSUYA, NAKAMURA JUMPEI, SHIBATA HIROKI, YAMAZAKI KEIJI, GO, NOBUAKI, HANAFUSA, TATSUYA, NAKAMURA, JUMPEI, SHIBATA, HIROKI, YAMAZAKI, KEIJI
Applicants: SHOWA DENKO KK, SHOWA DENKO K.K.
Application year: 1994
Main classification: F28D1
IPC codes: F28F27, F25B39, F28F3, F28D1